Elevation Of Ambient Temperature Research Articles

Alpha Adrenergic Regulation of Celiac Blood Flow and Plasma Catecholamine Response During Acute Heat Stress in Fed Cockerels

Hubbard cockerels with chronically implanted electromagnetic blood flow probes on the celiac artery were used to establish a relationship between changes in postprandial celiac mean blood flow (MBF) and plasma catecholamines during a acute heat exposure. Five min after the elevation of ambient temperature from 25 to 37 C, there were concomitant reductions (P<.05) in celiac MBF, norepinephrine (NE), and heart rate (HR). After 50 min of heat stress, rectal temperature (Tr), respiratory rate (RR), plasma epinephrine (E), and celiac vascular resistance (CVR) were significantly greater (P<.05) than preheat stress thermoneutral control values. During the thermoneutral recovery period, all parameters returned to values comparable to preheat exposure control with the exception of NE, which tended (P<.1) to remain lower.To determine the role of the sympathetic nervous system in regulating postprandial celiac MBF during acute heat exposure, chronically instrumented cockerels were infused with phenoxybenzamine, an α-adrenergic receptor-blocking agent. Alpha-receptor blockade attenuated both post-prandial intestinal hyperemia under thermoneutral conditions as well as the heat-induced reduction of postprandial celiac MBF. The results of these studies implicate the sympathetic nervous system in the regulation of postprandial celiac MBF in heat-stressed cockerels and indicate a possible α-adrenergic-mediated mechanism involved in postprandial intestinal hyperemia.

Influence of heating rate on control of heat loss from the tail in mice.

Although heating rate is important for stimulating thermoregulatory reflexes, it is not known if the control system differentiates between total heat gain and rate of heat gain. Exposing animals to microwaves inside a waveguide permits continuous monitoring of whole-body heat absorption. Tail skin temperature of restrained mice was recorded during whole-body exposure to 2,450-MHz microwave radiation at specific absorption rates (SAR) of either 11.5, 21.7, or 43.5 W . kg-1 and whole-body heat loads of 0.3-14 J . g-1. The integration of tail skin temperature with time, defined as the skin temperature index (STI), was measured as a function of absorbed heat load. At ambient temperatures of 20 and 25 degrees C the STI, averaged with respect to heat load, increased significantly with SAR. Depending on SAR, the sensitivity of heat loss from the tail to microwave exposure increased 32-71% per 1 degree C elevation in ambient temperature. The data indicate that heat loss from the tail increases with the whole-body heat load accrued from microwave exposure. When heat loss is averaged with respect to heat load, the rate of heat absorption and ambient temperature increase the sensitivity of thermoregulatory centers that control peripheral heat loss from the tail of mice.

Synthesis of a heat shock protein in the microvascular system of the rabbit brain following elevation of body temperature

Protein synthesis in the microvascular system of the rabbit brain was inhibited following the elevation of body temperature by 2−2.5°C. In , vivo labeling studies indicated that hyperthermia also induced the synthesis of a 74K protein in cerebral microvessels which is similar in molecular weight to one of the major heat shock proteins previously reported in tissue culture systems following elevation of ambient temperature. The present results suggest that a physiologically relevant increase in body temperature, similar to that attained during fever reactions, can induce the synthesis of a heat shock protein in the cerebral microvascular system of the intact mammal.

Translation of mRNA associated with monosomes and residual polysomes following disaggregation of brain polysomes by LSD and hyperthermia.

Intravenous administration of LSD to young adult rabbits induces a transient disaggregation of brain polysomes and a relocalization of mRNA from polysomes to monosomes. To analyze the spectrum of mRNA molecules which were associated with either the residual polysomes or the translationally inactive monosome complex, these two fractions were isolated on sucrose gradients and translated in a reticulocyte cell-free system. Analysis of [35S]methionine labeled translation products by one and two dimensional gel electrophoresis revealed that a full spectrum of mRNA molecules was relocalized from polysomes to monosomes following drug induced polysome disaggregation. The only exception was the mRNA coding for the LSD-induced 74K protein which was associated with the residual polysome fraction and not with the monosome complex. This brain protein is similar in molecular weight to one of the major 'heat shock' proteins which are induced in tissue culture cells following elevation of ambient temperature and disaggregation of existing polysomes. The mRNA coding for the 74K brain protein was not observed in polysomes isolated following blockage of LSD-induced hyperthermia but it was noted when hyperthermia was induced by elevation of ambient temperature. The mRNA species coding for the 74K protein was polyadenylated.

Comparison of the Effect of Intravenous Administration of d‐Lysergic Acid Diethylamide on Free and Membrane‐Bound Polysomes in the Rabbit Brain

The intravenous administration of LSD to young adult rabbits resulted in the disaggregation of both free and membrane-bound classes of brain polysomes. Based on the analysis of LSD dosage and the time course of the LSD-induced brain polysome shift, it was found that free polysomes were more sensitive to the drug than the membrane-bound polysome fraction. LSD-induced hyperthermia may be involved in the disaggregation of free and membrane-bound polysomes, since a correlation was found between the extent of LSD-induced hyperthermia and the degree of brain polysome shift. Prevention of LSD-induced hyperthermia by maintaining the animal at 4 degrees C blocked the disaggregation of both polysome classes. Induction of hyperthermia by elevation of ambient temperature also resulted in a shift in free and membrane-bound polysomes. In all cases the disaggregation of polysomes to monosomes was not caused by RNase activation. During polysome disaggregation, polyadenylated mRNA associated with both free and membrane-bound polysomes was not degraded but was relocalized from polysomes to monosomes.

Selective effects of LSD and hyperthemia on the synthesis of synaptic proteins and glycoproteins

Protein synthesis in rabbit brain was inhibited following the intravenous injection of LSD. The incorporation of [ 35S]methionine into brain microsomal and synaptic fractions was decreased by 35–45% relative to control values. A selective increase was observed, however, in the relative labeling of a protein of molecular weight 75,000. Our previous studies have shown that LSD induces an increase in body temperature (i.e. hyperthermia) in rabbits. When LSD-induced hyperthermia was blocked the general reduction in labeling of microsomal and synaptic proteins was still apparent but the selective increase in relative labeling of the 75,000 dalton protein was not. Induction of hyperthermia by means other than LSD (i.e. elevation of ambient temperature) produced selective increases in the relative labeling of microsomal and synaptic proteins of molecular weight 75,000 and 95,000. These proteins are similar in molecular weight to two of the major ‘heat shock’ proteins whose synthesis is induced in several cultured cell lines following elevation of ambient temperature. Fractionation of [ 35S]methionine-labeled synaptic membranes by lectin affinity chromatography and analysis of [ 35H]fucose labeling patterns indicated that, in contrast to the general reduction in labeling of brain proteins, the synthesis of synaptic glycoproteins was not altered by LSD. The synthesis of glycosylated proteins present in other subcellular fractions was, however, reduced. These results suggest that LSD induced selective changes in the synthesis of brain proteins and that the synthesis of synaptic glycoproteins may be relatively resistant to drug administration.

Hyperthermia and disaggregation of brain polysomes induced by bacterial pyrogen

Hyperthermia induced following injection of bacterial pyrogen to rabbits was associated with a disaggregation of brain polysomes to monosomes. Direct elevation of the body temperature to levels similar to that found after pyrogen administration also resulted in a brain polysome shift. The disaggregation of brain polysomes after either pyrogen injection or elevation of ambient temperature was not due to ribonuclease activation and the phenomenon was associated with a relocalization of polyadenylated mRNA from polysomes to monosomes. Since polysome disaggregation was not found in kidney, it appears that the brain may be more sensitive to elevations in body temperature.

Studies on the effect of heat exposure on lipid metabolism in rat: Modifications of lipids in plasma, erythrocytes and liver

1. 1.|It has been well established that cold exposure affects lipid metabolism. In this study, it is demonstrated that increasing ambient temperature, from 25 to 34°C, induces some variations in the lipid patterns of blood and liver in rats kept for several weeks in a thermostated room. 2. 2.|In the liver, some decrease in phospholipid and cholesterol content occurred, while the triglycerides showed a rise. In the plasma and red cells, total lipid, phospholipid and cholesterol levels fell. The free cholesterol:phospholipid molar ratio was significantly affected and following a simultaneous increase in plasma and decrease in red cells in the first days, values returned to normal after 2 weeks. 3. 3.|These effects are likely to be due to some alteration in the activity of the hypothalamo-hypophysothyroid axes, provoked by the elevation of ambient temperature.

Microwave Irradiation and Ambient Temperature Interact to Alter Rat Behavior Following Overnight Exposure

Each of twelve male hooded rats was trained to insert its head into a food cup for food pellets on a random-interval schedule of reinforcement. After performances stabilized, the rats were assorted into 3 groups of 4 animals. Groups were matched for response rates. Animals were exposed in groups of 4 for 15.5 h to CW 2450-MHz microwaves once every 6 nights. Animals of each group were exposed to microwaves at only one power density, either 5, 10, or 15 mW/cm2; they were exposed three times at an ambient temperature of 22 degrees C, then three times at 28 degrees C, and then once more at 22 degrees C. The relative humidity was 50% during all exposures. Rats were sham irradiated (at 0 mW/cm2) the night before each microwave exposure. Behavior was tested daily after termination of microwave irradiation or after sham exposures. None of the exposures to microwaves at 22 degrees C altered rates or durations of responding. Exposures at 28 degrees C reduced response rates and increased response durations in direct relation to the power density. The results are interpreted as the transient debilitation of behavior produced by the interaction of a mild elevation of ambient temperature and microwave irradiation.

Thermal Expansion of lnterlayer Spacing and Thermal Vibration of Carbon Atom in 3, 5-Xylenol-Formaldehyde Resin Carbon

The variation of c-axis spacing, c0, with the elevation of ambient temperature from room temperature to 900 C and the mean-square thermal vibrational displacement, Uv-2, of carbon atoms were studied on 3, 5-xylenol-formaldehyde resin carbon which is heat-treated at various temperatures up to 3000 C. X-ray diffractometer equipped with a high temperature furnace was used. The results were discussed in comparison with those of the problem coke.The value of ce increased linearly with the increase of ambient temperature. The coeffcient of thermal expansion, a, parallel to c-axis at 20 C increased from 2.7 10-5 C-1 to 2.8 10-5C with the increase of heat-treatment temperature (Fig.4). The value of increased with decrease of c9, the increase of Lc and the decrease of the strain along c-axis (Fig.5, 6 and 7). The value of u-v2 varied from O.015 A2 to O.012 A2 at 20 C with heat-treatment (Table 3). values for a for 3, 5-xylenol-formaldehyde resin carbon were smaller than those for petroleum coke heat-treated at various temperatures up to 3000 C and the values of Uv-2 were larger.